JP2005161547A - Inkjet head and inkjet recording apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inkjet head which can stably form a dot of a desired size on a recording medium, even if an ink droplet is continuously ejected at a high speed, and an inkjet recording apparatus. <P>SOLUTION: An ejection electrode 18, to which an ejection voltage for ejecting ink is applied, is formed on a head substrate 12. This can make an ejection port substrate 16 thin, and can make an ejection port 28 short. A surface, whereon an inner wall of the substrate 16 forming the ejection port 28 is brought into contact with the ink, is reduced for a decrease in friction, and the property of the ejection of the ink droplet from the ejection port 28 is improved. A charged coloring material particle in a main channel 30 is moved to the ejection port 28 by using an electric field which is directed upward in Fig. and generated from the ejection electrode 18 by a bias voltage, and a desired numbers of coloring material particles are concentrated in the ejection port 28. The dot of the desired size can be stably formed on the recording medium, even if the droplet is continuously ejected at the high speed. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an inkjet head that ejects ink to fly toward a recording medium, and an inkjet recording apparatus that records an image corresponding to image data on the recording medium using the inkjet head.

  The ink jet recording apparatus ejects ink from an ejection port and records an image corresponding to image data on a recording medium. As an ink jet recording apparatus, an electrostatic type, a thermal type, a piezo type or the like is known according to a difference in ink ejection control means.

  Hereinafter, an electrostatic ink jet recording apparatus will be described as an example. The electrostatic ink jet recording apparatus uses ink containing charged color material particles (colored charged particles) and applies a predetermined voltage to each discharge portion of the ink jet head in accordance with image data, thereby generating electrostatic force. The ejection of ink is controlled using this, and an image corresponding to the image data is recorded on the recording medium. As this electrostatic ink jet recording apparatus, for example, an ink jet recording apparatus disclosed in Patent Document 1 is known.

  FIG. 12 is a schematic configuration diagram of an example of an ink jet head of the electrostatic ink jet recording apparatus disclosed in Patent Document 1. The inkjet head 80 shown in the figure conceptually represents only one ejection portion of the inkjet head disclosed in Patent Document 1, and includes a head substrate 82, an ink guide 84, an insulating substrate 86, and a control. An electrode 88, a counter electrode 90, a DC bias voltage source 92, and a pulse voltage source 94 are provided.

  Here, the ink guide 84 is disposed on the head substrate 82, and a through hole (ejection port) 96 is formed in the insulating substrate 86 at a position corresponding to the arrangement of the ink guide 84. The ink guide 84 passes through the through hole 96, and its convex tip portion 84 a protrudes above the surface of the insulating substrate 86 on the recording medium P side. In addition, the head substrate 82 and the insulating substrate 86 are arranged at a predetermined interval, and a flow path 98 for the ink Q is formed between them.

  The control electrode 88 is provided in a ring shape on the surface of the surface of the insulating substrate 86 on the recording medium P side so as to surround the periphery of the through hole 96 for each ejection unit. The control electrode 88 is connected to a pulse voltage source 94 that generates a pulse voltage in accordance with image data. The pulse voltage source 94 is grounded via a DC bias voltage source 92.

  The counter electrode 90 is disposed at a position facing the tip end portion 84 a of the ink guide 84 and is grounded. The recording medium P is disposed on the surface of the surface of the counter electrode 90 on the ink guide 84 side. That is, the counter electrode 90 functions as a platen that supports the recording medium P.

  At the time of recording, the ink Q including the color material particles charged with the same polarity as the voltage applied to the control electrode 88 by an ink circulation mechanism (not shown) moves in the ink flow path 98 from the right side to the left side in the drawing. Circulated. Further, a high voltage of 1.5 kV, for example, is constantly applied to the control electrode 88 by the DC bias voltage source 92. At this time, a part of the ink Q in the ink flow path 98 passes through the through hole 96 of the insulating substrate 86 due to a capillary phenomenon or the like, and is concentrated on the tip portion 84 a of the ink guide 84.

  When, for example, a pulse voltage of 0 V is applied from the pulse voltage source 94 to the control electrode 88 biased to 1.5 kV by the bias voltage source 92, 1.5 kV in which both voltages are superimposed is applied to the control electrode 88. Applied. In this state, the electric field strength in the vicinity of the tip portion 84 a of the ink guide 84 is relatively low, and the ink Q containing the color material particles concentrated on the tip portion 84 a of the ink guide 84 jumps out of the tip portion 84 a of the ink guide 84. Absent.

  On the other hand, when a pulse voltage of 500 V, for example, is applied from the signal voltage source 94 to the control electrode 88 biased to 1.5 kV, 2 kV on which both voltages are superimposed is applied to the control electrode 88. As a result, the ink Q containing the coloring material particles concentrated on the tip portion 84a of the ink guide 84 is ejected as an ink droplet R from the tip portion 84a by electrostatic force, and is pulled by the grounded counter electrode 90 to be recorded. Adhering onto P, dots of colorant particles are formed.

  In this way, recording is performed with dots of color material particles while relatively moving the inkjet head 80 and the recording medium P supported on the counter electrode 90, whereby an image corresponding to the image data is recorded on the recording medium P. Is done.

  By the way, in the electrostatic ink jet head, when a plurality of ejection portions are arranged in a matrix and a multi-channel head is configured, it is gradually difficult to connect the signal wiring to the control electrode (ejection electrode) of each ejection portion. . For this reason, when the number of channels is large, it can be considered that the insulating substrate is formed into a multilayer wiring structure to connect the signal wiring to the ejection electrode. Therefore, as the number of channels increases in the future, the thickness of the insulating substrate tends to gradually increase.

  However, as the insulating substrate becomes thicker, its length becomes longer than the opening diameter of the through-hole (discharge port), so the resistance between the ink and the inner wall of the through-hole increases, and the ink is discharged from the through-hole. It becomes difficult to be discharged. Further, when the insulating substrate is thick, the ink may stay in the through hole depending on the speed of the ink flow, which makes it difficult to supply the ink to the tip portion of the ink guide. As a result, there is a problem that the response to the discharge frequency is deteriorated, and the dot diameter is gradually reduced as the drawing frequency is increased.

  Further, when the drawing frequency is increased, the following problem also occurs. When the inkjet head is driven to record an image on a recording medium, a drawing signal voltage is applied to the ejection electrode at the timing shown in FIG. 13 according to the recorded image. Since a constant bias voltage is applied to the ejection electrode as described above, when no drive voltage is applied to the ejection electrode (OFF state in the figure) in the timing chart shown in FIG. The colorant particles in the ink are replenished to the discharge port by the electrostatic force due to the voltage. On the other hand, when a driving voltage is applied to the ejection electrode (ON state in the figure), the ink in which the color material particles are sufficiently concentrated is ejected as ink droplets from the ejection port. In order to draw at high speed, it is necessary to shorten the pulse width of the drive voltage applied to the ejection electrode, and accordingly, the time for supplying ink particles to the ejection port is also shortened. As a result, the supply of ink particles to the ejection port becomes insufficient, the dot diameter becomes small, and the dot diameter cannot be formed stably.

In addition to the electrostatic type, when the insulating substrate becomes thick, that is, when the length of the through hole becomes long, the same problem occurs in the ink jet recording apparatus using various types of ink jet heads. .
JP 10-138493 A

  The object of the present invention is to eliminate the problems based on the above-mentioned conventional technology, improve the ink supply to the ejection port, and stabilize the dots of the desired size even when ink droplets are ejected continuously at high speed. Thus, an inkjet head and an inkjet recording apparatus that can be formed on a recording medium are provided.

  In order to solve the above problems, a first aspect of the present invention is an ink jet head that ejects ink as ink droplets using electrostatic force and flies toward a recording medium. An ejection port substrate having an ejection port to be ejected; a head substrate disposed at a predetermined distance from the ejection port substrate; and a position facing the ejection port of the head substrate, An inkjet head including an ejection electrode to which an ejection voltage for ejection is applied is provided.

  In the inkjet head according to the aspect of the invention, it is preferable that the ejection electrode is formed on a surface of the head substrate on a side facing the ejection port substrate or inside the head substrate.

  In the present invention, the discharge electrode is composed of a first discharge electrode and a second discharge electrode, and the first discharge electrode and the second discharge electrode are arranged substantially coaxially and spaced apart from each other by a predetermined interval. It is preferable.

  In the ink jet head of the present invention, it is preferable that the discharge electrode has a ring shape.

  The head substrate includes an ink guide weir for guiding the ink to the discharge port in the vicinity of a position facing the discharge port, and the discharge electrode is formed on the ink guide weir. preferable.

  In the ink jet head of the present invention, it is preferable that the ink guide weir has an inclined surface, and a ring-shaped ejection electrode is formed on the inclined surface.

  In the inkjet head according to the aspect of the invention, it is preferable that an ink guide groove connected to the discharge port is formed on a surface of the discharge port substrate facing the head substrate. It is preferable that the groove depth is deeper toward the discharge port.

  The inkjet head of the present invention includes an ink guide that is provided at a position of the head substrate facing the discharge port of the discharge port substrate, and has a tip that penetrates the discharge port. The discharge electrode includes the ink guide and the ink guide. It is preferable to form so as to surround the periphery of the connection portion with the head substrate.

  In the inkjet head according to the aspect of the invention, it is preferable that a ratio between the inner diameter of the ejection electrode and the distance from the ejection electrode to the tip of the ink guide is in a range of 1: 0.5 to 1: 2.

  The inkjet head of the present invention further includes a guard electrode for shielding an electric field generated from the ejection electrode, and the guard electrode is preferably formed at a position closer to the recording medium than the ejection electrode, The guard electrode is preferably formed inside the ejection substrate.

  The inkjet head of the present invention further includes a power source for applying a discharge voltage to the discharge electrode, and a wiring connected to the power supply from the discharge electrode is a side of the head substrate facing the discharge port substrate. It is preferable that it is formed on the surface opposite to the surface.

  In order to solve the above problems, a second aspect of the present invention provides an ink jet recording apparatus including the ink jet head according to the first aspect of the present invention.

  Since the inkjet head of the present invention is provided with ejection electrodes on the head substrate instead of the ejection port substrate, the ejection port substrate can be made thinner than before, and the length of the ejection port can be made shorter than before. Can do. For this reason, the resistance between the ink and the inner wall of the ejection port is also reduced, and ink can be ejected quickly from the ejection port. Further, the ink is prevented from staying in the through hole due to the speed of the ink flow. Further, since the discharge electrode is provided on the head substrate, the discharge electrode is generated by applying a bias voltage to the ink in the flow path defined by the head substrate and the discharge port substrate. An electric field directed toward the ejection port acts, and the colorant particles in the ink are quickly concentrated at the ejection port. Therefore, the response of the ejection frequency during image recording is improved, and even if dots are drawn continuously at high speed, the dot diameter can be prevented from becoming smaller, so that dots of a desired size can be drawn stably. can do.

  Further, by providing the ejection electrode on the head substrate, it is possible to form the signal wiring connected to the ejection electrode on the back surface of the head substrate (the surface opposite to the surface facing the ejection port substrate). For this reason, when a multi-channel head is configured by arranging a plurality of ejection portions in a matrix, signal wiring connected to the ejection electrodes of each ejection portion may be formed in a multilayer structure on the back surface of the head substrate. A multi-channel head can be realized while the discharge port substrate is made thin.

  In addition, since the ink jet head of the present invention can include an ink guide weir or an ink guide groove, the ink in the flow path formed by the head substrate and the discharge substrate is along the ink guide weir or the ink guide groove. The ink is promptly guided to the ejection port, and the ink supply to the ejection port can be further improved.

  Since the ink jet recording apparatus of the present invention includes the ink jet head of the present invention, dots of a desired size can be formed on a recording medium at high speed and stably, and high quality images can be drawn at high speed. It is.

  Hereinafter, an ink jet head and an ink jet recording apparatus of the present invention will be described in detail based on preferred embodiments shown in the accompanying drawings.

FIG. 1 is a schematic cross-sectional view showing a schematic configuration of an example of the ink jet head of the present invention. FIGS. 2A and 2B are views taken along arrows AA and BB in FIG. Are shown respectively.
The electrostatic ink jet head 10 shown in FIG. 1 includes a head substrate 12, an ink guide 14, and an ejection port substrate 16 having ejection ports 28. A shield plate 22 for shielding electric field noise from the outside is disposed on the lower surface of the head substrate 12 (the surface opposite to the surface facing the discharge port substrate 16). The discharge port substrate 16 includes an insulating substrate 32, a guard electrode 20, and an insulating layer 34, and the guard electrode 20 and the insulating layer 34 are sequentially arranged on the opposite side of the insulating substrate 32 facing the head substrate 12. Are stacked.
The head substrate 12 and the discharge port substrate 16 are arranged to be spaced apart from each other at a predetermined interval. The head substrate 12 and the discharge port substrate 16 define a main flow path 30 for supplying ink to each discharge port 28, and the main flow path 30 and the discharge port 28 (up to the opening end on the discharge side) define the ink flow. A path is formed.

  Further, a counter electrode 24 that supports the recording medium P and a charging unit 26 of the recording medium P are disposed at a position facing the ejection portion of the inkjet head 10.

  Such an ink jet head 10 includes an ink Q formed by dispersing fine particles (hereinafter referred to as color material particles) containing a color material component such as a pigment in an insulating liquid (carrier liquid). The ink is ejected by electrostatic force, and the ink droplet is modulated and ejected according to the image data by turning on / off the driving voltage applied to the ejection electrode 18 according to the image data (ejection on / off). Then, an image is recorded on the recording medium P.

As shown in FIG. 2, the inkjet head 10 has a multi-channel structure in which each discharge portion (nozzle (discharge port 28)) is two-dimensionally arranged in order to perform higher-density image recording. However, in FIG. 1, only one ejection part is shown in order to clearly show the configuration.
In the inkjet head 10 of the present invention, the number of discharge electrodes, the physical arrangement, and the like can be freely selected. For example, not only a multi-channel structure as shown in the figure but also one having only one row of ejection portions may be used. Further, a so-called (full) line head having a row of ejection units corresponding to the entire area of the recording medium P may be used, or a so-called serial head (shuttle type) that is scanned in a direction orthogonal to the direction of the nozzle row. Good. The ink jet head of the present invention can be used for both monochrome and color recording apparatuses.

In the ink jet head 10 of the illustrated example, the ink guide 14 is made of a ceramic flat plate having a projecting tip portion 14a and having a predetermined thickness, and is disposed on the head substrate 12 for each ejection portion.
An ejection port 28 for ejecting ink droplets R is formed through the ejection port substrate 16 described later. The ink guide 14 is disposed corresponding to each ejection port 28 (ejection unit), passes through the ejection port 28, and a tip portion 14 a of the surface on the recording medium P side of the ejection port substrate 16 (insulating layer 34). It protrudes above the upper surface (hereinafter, for convenience, this side is the upper side and the other is the lower side). Note that a cutout serving as an ink guide groove for collecting the ink Q in the tip end portion 14a may be formed in the center portion of the ink guide 14 in the vertical direction in the drawing by capillary action.

In the illustrated example, the end portion 14a side of the ink guide 14 is formed into a substantially triangular shape (or trapezoid) that gradually becomes thinner toward the counter electrode 24 side. The shape of the ink guide 14 is not particularly limited as long as the ink Q, in particular, the charged fine particle component in the ink Q can be concentrated through the discharge port 28 of the discharge port substrate 16 to the tip portion 14a. For example, the tip portion 14a may be changed as appropriate, such as not having a protrusion, or may have a conventionally known shape.
Here, it is preferable that the metal is deposited on the most distal portion of the ink guide 14. By depositing metal on the most distal portion, the dielectric constant of the tip portion 14 a of the ink guide 14 is substantially increased, It becomes easy to generate a strong electric field, and ink ejection properties can be improved.

  On a surface (bottom surface) opposite to the side facing the discharge port substrate 16 of the head substrate 12, a shield plate 22 for shielding electrolytic noise from the outside is disposed as a preferred mode. The shield plate 22 is a grounded conductive flat plate, can eliminate the adverse effect on the electric field formation of the discharge portion, and can maintain a stable drawing performance.

As described above, the head substrate 12 and the discharge port substrate 16 are spaced apart from each other by a predetermined distance, and the main flow path 30 is formed by a gap therebetween. The main flow path 30 functions as an ink reservoir (ink chamber) for supplying the ink Q to the ejection port 28 (ink guide 14).
The ink Q is recorded at a predetermined speed (for example, an ink flow rate of 200 mm / s) from the right to the left in the drawing in a predetermined direction, in the illustrated example, in the main flow path 30 by an ink circulation mechanism (not shown) during image recording. ).

The discharge port substrate 16 is configured by laminating the guard electrode 20 and the insulating layer 34 on the upper surface of the insulating substrate 32 (the surface opposite to the side facing the head substrate 12). In the discharge port substrate 16, a discharge port 28 for discharging the ink droplet R is formed through the insulating substrate 32. The ink guides 14 are inserted into the respective ejection ports 28 of the ejection port substrate 16 with their tips protruding upward. In the discharge port substrate 16 having such a structure, for example, the guard electrode 20 is formed on the upper surface of the insulating substrate 32 made of an insulating material, and then the upper surface of the guard electrode 20 and a part of the upper surface of the insulating substrate 32 are formed. The insulating layer 34 can be formed so as to cover it.
The ink jet head of the present invention shown in FIG. 1 has a structure in which the ejection electrode 18 is exposed to the main flow path 30 and is in contact with the ink Q, so that the ejection characteristics of the ink droplets are greatly improved. This point will be described later together with the action of discharge.

  As shown in FIG. 1, ejection electrodes 18 are formed on the head substrate 12 of the inkjet head 10 of the present invention. The ejection electrode 18 is arranged on the upper surface of the head substrate 12 (the surface facing the ejection port substrate 16) as a ring-shaped circular electrode surrounding the periphery of the connection portion between the ink guide 14 and the head substrate 12. Yes. The ejection electrode 18, the ink guide 14, and the ejection port 28 are positioned so that they are substantially coaxial. Here, the discharge electrode 18 is formed on the surface of the head substrate 12 so as to be exposed to the main flow path 30. However, the present invention is not limited thereto, and as shown in FIG. You may form in the position which becomes substantially coaxial with the discharge outlet. The ejection electrode 18 is connected to a signal voltage source 33. The signal voltage source 33 is a drive voltage (for example, pulse voltage) having a predetermined potential corresponding to ejection data (ejection signal) such as image data and print data. Can be generated.

  The head substrate having such a structure is produced, for example, by forming the ejection electrode 18 on the head substrate 12 on which the ink guide 14 is formed using, for example, a semiconductor manufacturing technique using photolithography. can do. Alternatively, the discharge electrode 18 is formed on the flat first substrate using a semiconductor manufacturing technique using photolithography, and then a through hole for inserting the ink guide is formed in the central portion of the discharge electrode 18. . Then, the first substrate can be mounted on the second substrate while the ink guide of the second substrate is inserted into the through hole of the first substrate, and can be manufactured by sticking them together.

  As described above, the illustrated example has a multi-channel structure in which the discharge ports 28 are two-dimensionally arranged. Therefore, as shown in FIG. Two-dimensionally arranged corresponding to the discharge ports 28. The wiring connected from the ejection electrode 18 to the signal voltage source 33 can be formed, for example, on the lower surface of the head substrate 12. Furthermore, since the layers for forming the wiring can be laminated, the wiring can be formed extremely easily even when the discharge electrode 18 is formed on the discharge port substrate 16 even in the multi-channel structure.

  By the way, since the conventional inkjet head has the discharge electrode 88 provided on the discharge port substrate 86 as shown in FIG. 12, for example, when a drive voltage is applied to the discharge electrode 88, the discharge head is only from the upper surface of the discharge electrode 88. In addition, an electric field is also generated from the lower surface of the ejection electrode 88. That is, an electric field in the direction from the ejection port 96 toward the head substrate surface 82 acts on the ink Q circulating in the main flow path. The electric field generated in the direction perpendicular to the head substrate surface 82 from the lower surface of the ejection electrode 88 acts to prevent the ink particles contained in the ink Q circulating in the main flow path from moving toward the ejection port 96. For this reason, when a driving voltage is applied to the ejection electrode 88, the ink particles are prevented from concentrating at the ejection ports 96, and a certain time is required until the ink particles are sufficiently concentrated at the ejection ports 96.

However, since the inkjet head of the present invention shown in FIG. 1 has the ejection electrode 18 provided on the head substrate 12, only the electric field generated from the upper surface side of the ejection electrode 18 can act on the ink particles. That is, since there is no electric field that prevents the ink particles from being concentrated at the ejection port 28, the ink particles can be quickly concentrated at the ejection port 28.
Furthermore, since the discharge electrode 18 is formed not on the discharge port substrate 16 but on the head substrate 12, the thickness of the discharge port substrate 16 can be made thinner than before. For this reason, the length of the ejection port can be made shorter than before, the resistance between the ink and the inner wall of the ejection port is reduced, and ink can be ejected quickly from the ejection port. Furthermore, the ink can be prevented from staying in the through hole due to the speed of the ink flow.

  The ejection electrode 18 is not limited to a ring-shaped circular electrode, and various shapes of electrodes can be used. Preferably, a surrounding electrode arranged so as to surround the outer periphery of the connection portion of the ink guide 14 with the head substrate 12 is exemplified (a part of the surrounding electrode may be cut out). Among them, a substantially circular electrode is preferable. More preferably, it is a circular electrode.

  In the present invention, the inner diameter of the ejection electrode 18 and the distance from the surface of the ejection electrode 18 to the tip of the ink guide 14 are preferably in the range of 1: 0.5 to 1: 2. It is much more preferable that it exists in the range of 7-1: 1.7. That is, when the inner diameter of the discharge electrode 18 is r and the distance from the surface of the discharge electrode 18 to the tip of the ink guide 14 is h, h / r is in the range of 0.5 to 2. More preferably, it is preferable to adjust at least one of the inner diameter of the discharge electrode 18 and the distance from the surface of the discharge electrode 18 to the tip of the ink guide so as to be within the range of 0.7 to 1.7. This is because the electric field formed by the ejection electrode 18 converges and the region where the strongest electric field is formed is within the range, and the tip of the ink guide, which is the ejection position, is arranged at a position that satisfies the range. As a result, even when the voltage applied to the ejection electrode 18 is lower than in the prior art, it is possible to reliably eject droplets from the tip of the ink guide. That is, the voltage applied to the ejection electrode can be reduced.

  Here, as the inner diameter of the surrounding electrode that is not a constant inner diameter, such as a substantially circular electrode, an effective inner diameter such as an average inner diameter that can be regarded as a substantially inner diameter may be used. Further, when a parallel electrode is used as the discharge electrode, the inner diameter of the discharge electrode may be the interval between the parallel electrodes, and when a substantially parallel electrode is used, it can be regarded as a substantially interval such as an average interval. The effective interval may be used.

The guard electrode 20 is provided at a position closer to the recording medium P than the discharge electrode 18, and electric lines of force generated from the discharge electrode 18 are arranged at the discharge port adjacent to the discharge port 28 corresponding to the discharge electrode 18. The ink guide is positioned so as not to reach the tip of the ink guide. Here, the guard electrode 20 is formed on the upper surface of the discharge port substrate 16, and the surface thereof is covered with the insulating layer 34. As shown in FIG. 2A, the guard electrode 20 is a sheet-like electrode common to each discharge electrode such as a metal plate, and the opening 36 corresponding to each discharge port 28 arranged two-dimensionally. Is perforated.
The guard electrode 20 can shield electric field lines between the adjacent ejection electrodes 18 and suppress electric field interference between the adjacent ejection electrodes. A predetermined voltage is applied to the guard electrode 20 (including 0 V due to grounding), and in the illustrated example, the guard electrode 20 is grounded to 0 V.

Here, the guard electrode 20 is a tip portion of an ink guide (hereinafter referred to as “own channel” for convenience) disposed in a corresponding discharge port 28 which is a discharge portion among electric lines of force generated from the discharge electrode 18. And the electric lines of force from the other discharge electrodes 18 and the tip of the ink guide 14 disposed in the other discharge ports 28 (referred to as “other channels”). It is necessary to provide it so as to shield the electric lines of force.
In the absence of the guard electrode 20, the lines of electric force generated from the inner periphery of the discharge electrode 18 converge inside the discharge electrode 18 and act on the own channel to generate a necessary electric field. On the other hand, the lines of electric force generated from the outer peripheral portion of the ejection electrode 18 diverge to the outside and affect other channels, resulting in electric field interference.

  Considering the above points, the diameter of the opening 36 of the guard electrode 20 is preferably larger than the inner diameter of the discharge electrode 18 of the own channel so as not to block the electric lines of force to the own channel. That is, the end portion of the guard electrode 20 on the discharge port 28 side (hereinafter, the discharge port side end portion of each member is referred to as “inner edge portion” and the opposite end portion is referred to as “outer edge portion”). It is preferable to be separated (retracted) from the discharge port 28 rather than the inner edge portion.

In order to efficiently shield the lines of electric force to other channels, the diameter of the opening 36 of the guard electrode 20 is preferably smaller than the outer diameter of the discharge electrode 18 of the own channel. That is, it is preferable that the inner edge portion of the guard electrode 20 is closer (advanced) to the discharge port 28 than the outer edge portion of the discharge electrode 18 of the own channel.
By having the above-described configuration, the ejection stability from the ejection port 28 is sufficiently ensured, and variations in the ink landing position due to electric field interference between adjacent channels are suitably suppressed, and the stability can be increased. It is possible to perform image recording with high image quality.

  In the above example, the discharge electrode 18 is described as a circular electrode. However, when the discharge electrode 18 is not a circular electrode, an effective diameter that can be regarded as a substantial diameter, such as an average diameter, may be considered depending on the shape. Alternatively, the opening 36 of the guard electrode 20 is substantially similar to the inner peripheral side shape or the outer peripheral side shape of the discharge electrode 18, and the inner edge of each of the discharge electrodes 18 in the circumferential direction is the discharge electrode of the own channel. The guard electrode 20 may be provided so as to be separated (retracted) from the discharge port 28 rather than the inner edge portion of 18 and to approach (advance) the discharge port 28 from the outer edge portion (that is, the opening 36 of the guard electrode 20). May be formed).

In the above example, the guard electrode 20 is a sheet-like electrode. However, the present invention is not limited to this, and the guard electrode 20 may be provided so as to shield the electric lines of force of the other channels between the discharge units. Anything is acceptable. For example, the guard electrode 20 may be provided in a mesh shape between the respective discharge units, or may not be provided in a portion that is sufficiently distant from the discharge unit so as not to cause electric field interference. It may be provided only between.
Even in such a case, the inner edge of the discharge electrode 18 of the own channel is farther from the discharge port 28 than the inner edge of the discharge electrode 18 and is closer to the discharge port 28 than the outer edge of the discharge electrode 18. Thus, the guard electrode 20 may be formed.

As described above, in FIG. 1, the counter electrode 24 is disposed so as to face the ejection surface of the ink droplet R of the inkjet head 10.
The counter electrode 24 is disposed at a position facing the front end portion 14a of the ink guide 14, and is disposed on the grounded electrode substrate 24a and the lower surface of the electrode substrate 24a in the drawing, that is, the surface on the inkjet head 10 side. The insulating sheet 24b is used.
The recording medium P is supported by, for example, electrostatic adsorption on the lower surface of the counter electrode 24 in the drawing, that is, the surface of the insulating sheet 24b, and the counter electrode 24 (insulating sheet 24b) serves as a platen of the recording medium P. Function.

At least during recording, the recording medium P held on the insulating sheet 24b of the counter electrode 24 by the charging unit 26 is a predetermined negative high voltage having a polarity opposite to that of the drive voltage (for example, pulse voltage) applied to the ejection electrode 18. For example, it is charged to -1.5 kV.
As a result, the recording medium P is negatively charged and biased to a negative high voltage, acts as a substantial counter electrode with respect to the ejection voltage 18, and is electrostatically adsorbed to the insulating sheet 24 b of the counter electrode 24.

  The charging unit 26 includes a scorotron charger 26a for charging the recording medium P to a negative high voltage, and a bias voltage source 26b for supplying a negative high voltage to the scorotron charger 26a. The charging means of the charging unit 26 used in the present invention is not limited to the scorotron charger 26a, and various discharging means such as a corotron charger, a solid charger, and a discharge needle can be used.

In the illustrated example, the counter electrode 24 includes an electrode substrate 24a and an insulating sheet 24b, and the recording medium P is charged to a negative high voltage by the charging unit 26, whereby a bias voltage is applied to the counter electrode. However, the present invention is not limited to this, and the counter electrode 24 is constituted only by the electrode substrate 24a, and the counter electrode 24 (electrode substrate 24a itself) is formed. May be connected to a negative high voltage bias voltage source so as to be constantly biased to a negative high voltage so that the recording medium P is electrostatically attracted to the surface of the counter electrode 24.
Further, the electrostatic adsorption of the recording medium P to the counter electrode 24 and the charging of the recording medium P to a negative high voltage or the application of a negative bias high voltage to the counter electrode 24 are separate negative high voltage sources. The support of the recording medium P by the counter electrode 24 is not limited to the electrostatic adsorption of the recording medium P, and other support methods and support means may be used.

  Hereinafter, the present invention will be described in more detail by explaining the operation of ejecting ink droplets R in the inkjet head 10.

In the ink jet head 10 shown in FIG. 1, an ink containing colorant particles charged to the same polarity, for example, positive (+), as the voltage applied to the ejection electrode 18 by an ink circulation mechanism including a pump (not shown) at the time of recording. Q is circulated in the main flow path 30 in the direction of the arrow (from the right to the left in the figure).
On the other hand, at the time of recording, the recording medium P is supplied to the counter electrode 24 and charged by the charging unit 26 to the opposite polarity of the color material particles, that is, negative high voltage (for example, −1500 V) and charged with the bias voltage. Thus, it is electrostatically attracted to the counter electrode 24. The shield plate 22 is grounded.
In this state, the recording medium P (counter electrode 24) and the inkjet head 10 are relatively moved, and a driving voltage (pulse voltage) is applied from the signal voltage source 33 to each ejection electrode 18 according to the supplied image data. And the ink droplet R is modulated and ejected according to the image data, and the image is recorded on the recording medium P.

Here, in a state where the drive voltage is not applied to the ejection electrode 18 (or in a state where the applied voltage is at a low voltage level), that is, in a state where only the bias voltage is applied, the ink Q has a bias voltage and The Coulomb attractive force with the charge of the color material particles (charged particles) of the ink Q, the Coulomb repulsion force between the color material particles, the viscosity of the carrier liquid, the surface tension, the dielectric polarization force, etc. act, and these are coupled to produce the color. The material particles and the carrier liquid move and are balanced in a meniscus shape slightly raised from the discharge port 28 as conceptually shown in FIG.
In addition, the colorant particles move toward the recording medium P charged with a bias voltage by so-called electrophoresis due to the Coulomb attractive force or the like. That is, the ink Q is concentrated at the meniscus of the discharge port 28.

  From this state, a drive voltage is applied to the ejection electrode 18. As a result, the drive voltage is superimposed on the bias voltage, and the movement coupled by the superposition of the drive voltage further occurs in the previous coupling, and the color material particles and the carrier liquid are biased (counter electrode) side by the electrostatic force. That is, when pulled to the recording medium P side, the meniscus grows to form a substantially conical ink liquid column so-called tailor cone from its upper part. Similarly to the above, the color material particles are moved to the meniscus by electrophoresis, and the ink Q of the meniscus is concentrated and is in a substantially uniform high density state having a large number of color material particles.

When a finite time has passed after the start of the application of the drive voltage, the balance between the color material particles and the surface tension of the carrier liquid mainly breaks at the tip of the meniscus with high electric field strength due to the movement of the color material particles, The meniscus grows abruptly to form a slender ink liquid column having a diameter of about several μm to several tens of μm, which is called a kite string.
Further, when a finite time elapses, the silk thread grows, and the growth of the silk thread, vibration caused by Rayleigh / Weber instability, uneven distribution of colorant particles in the meniscus, uneven distribution of electrostatic field on the meniscus, etc. As a result of this interaction, the kite string is divided, ejected / flyed as ink droplets R, and pulled by the bias voltage to land on the recording medium P. It should be noted that the growth and splitting of the kite and the movement of the color material particles to the meniscus (spinner) occur continuously during the application of the drive voltage.
Further, when the application of the driving voltage is finished (discharge is turned off), the state returns to the state of the meniscus to which only the bias voltage is applied.

Here, in the inkjet head 10 of the present invention, the upper surface of the ejection electrode 18 is exposed to the main flow path 30, that is, in contact with the ink Q in the main flow path 30.
As described above, when a drive voltage is applied to the discharge electrode 18 in contact with the ink Q in the ink flow path formed by the main flow path 30 and the discharge port 28 (up to the opening end) (discharge on), Part of the supplied charge is injected into the ink Q, and the conductivity of the ink Q located between the ejection port 28 and the ejection electrode 18 is increased. The charged color material particles floating between the ejection port 28 and the ejection electrode 18 are pushed up toward the ejection port 28 by the electrostatic force from the ejection electrode 18. As a result, in the ink jet head 10 of the present invention, the ink Q is remarkably easy to eject the ink droplet R only when the drive voltage is applied to the ejection electrode 18 (when ejection is on) (ejection). Improved).

The electrostatic ink jet having the above configuration stably discharges ink droplets even when the driving voltage applied to the discharge electrode 18 for discharging ink droplets is significantly lower than that of the conventional case. Can do. According to the study of the present inventor, as an example, even if a conventional electrostatic ink jet head has a bias voltage of −1500 V and a drive voltage of 1000 V is required, For example, the ink droplet R can be stably discharged with a driving voltage of about 400V. Therefore, according to the ink jet head shown in the present embodiment, it is possible to stably control the ejection of ink droplets on / off by using an inexpensive power source and on / off of a low driving voltage.
In addition, by improving the discharge property, the bias voltage applied to the recording medium P (counter electrode 24) is lowered and / or even when using a low discharge property ink (for example, low conductivity ink) Without increasing the drive voltage, it is possible to perform stable ejection while ensuring sufficient ink droplet ejection properties when ejection is on. That is, it is possible to reduce the discharge performance when the discharge is turned off while ensuring the discharge performance when the discharge is turned on. Therefore, according to the present invention, it is possible to greatly expand the difference in dischargeability between when discharge is on and when discharge is off, and to discharge ink droplets more stably.

  In addition, according to the present invention, since the drive voltage can be lowered, the electric field interference between the adjacent ejection electrodes 18 can also be reduced. Furthermore, according to the above configuration, it is possible to prevent a short circuit and a discharge between the discharge electrode 18 and the guard electrode 20 due to the coating of the color material particles of the ink.

In FIG. 4, the conceptual diagram of another example of the inkjet head of this invention is shown.
The inkjet head 110 shown in FIG. 4 differs from the inkjet head 10 shown in FIG. 1 only in the structure of the head substrate. Therefore, the same reference numerals are given to the same members, and the following description mainly focuses on the differences. Do.

The inkjet head of FIG. 4 is a two-layer electrode type inkjet head in which the ejection electrode 18 of the inkjet head shown in FIG. 1 is composed of two layers of a first ejection electrode 18a and a second ejection electrode 18b. The inkjet head 110 includes a first ejection electrode 18 a, an insulating layer 35, a second ejection electrode 18 b, and an ink guide 14 on the head substrate 12. The first ejection electrode 18a and the second ejection electrode 18b are both ring-shaped circular electrodes, and are arranged substantially coaxially with the ink guide 14 and spaced apart from each other by a predetermined distance. As shown in FIG. 4, an insulating layer 35 is formed between the first ejection electrode 18a and the second ejection electrode 18b in order to prevent contact between both electrodes. Here, the second discharge electrode is exposed to the main flow path 30, but an insulating layer for protecting and planarizing the surface of the second discharge electrode may be formed on the surface of the second discharge electrode. Good.
The first discharge electrode 18a and the second discharge electrode 18b are not limited to ring-shaped circular electrodes, and may be, for example, a substantially circular electrode, a divided circular electrode, or the like as long as the electrodes are arranged substantially coaxially with the ink guide 14. Any shape of electrode such as a parallel electrode or a substantially parallel electrode may be used.
FIGS. 5A and 5B are views taken along lines AA and BB in FIG. 4, respectively. As shown in FIG. 5A, the 15 ejection units are arranged in 5 rows (1 column, 2 columns, 3 columns, 4 columns, 5 columns) per row in the row direction (sub-scanning direction). Three (A row, B row, C row) are arranged in a matrix form per column in the direction (main scanning direction).

  As shown in FIG. 5A, the first ejection electrodes 26 of the three ejection sections arranged in the first column are connected to each other. The same applies to the second to fifth columns. Further, as shown in FIG. 5B, the second ejection electrodes 28 of the five ejection sections arranged in the A row are connected to each other. The same applies to the B and C rows. The first discharge electrode 18a and the second discharge electrode 18b are each connected to a control means (not shown) that outputs a discharge voltage corresponding to the image data.

  In addition, the five ejection units in the A row are arranged at a predetermined interval in the row direction. The same applies to the B and C rows. Further, the five ejection units in the B row are spaced apart from the five ejection units in the A row by a predetermined interval in the column direction, and 5 A in the A row in the row direction. It arrange | positions between one discharge part and the five discharge parts of C line. Similarly, the five discharge units in the C row are spaced apart from the five discharge units in the B row by a predetermined interval in the column direction, and each of the B row in the row direction. It arrange | positions between five discharge parts and the five discharge parts of A line.

  As described above, the five ejection units included in each of the rows A, B, and C are arranged so as to be shifted in the row direction, so that one row recorded on the recording medium P is divided into three in the row direction.

  At the time of recording an image, the three first ejection electrodes 26 arranged in the same column are simultaneously driven to the same voltage level. Similarly, the five second ejection electrodes 28 arranged in the same row are simultaneously driven to the same voltage level. Further, one row recorded on the recording medium P is divided into three groups corresponding to the number of rows of the second ejection electrodes 18b in the row direction, and is sequentially recorded in a time division manner. For example, in the example shown in FIG. 5, an image for one line is recorded on the recording medium P by sequentially recording the A line, the B line, and the C line of the second ejection electrode 28.

  In the above example, an inkjet head having a two-layer electrode structure in which the first discharge electrode 18a and the second discharge electrode 18b are provided on the head substrate 12 is used. An inkjet head having a multi-layer discharge electrode structure provided with an ink jet head may be used.

FIG. 6 shows a schematic configuration diagram of still another example of the ink jet head according to the present invention.
The ink jet head 120 is the same as the ink jet head shown in FIG. 1 except that an ink guide groove 52 leading from the upstream side of the ink flow to the through hole 28 is formed on the surface of the discharge port substrate 16 facing the head substrate 12. Has the same structure. In the ink jet head shown in FIG. 6, the same members as those in the ink jet shown in FIG. 6A is a schematic cross-sectional view of the ejection portion of the inkjet head 120, and FIG. 6B is a schematic plan view when the ejection portion of the inkjet head shown in FIG. 6A is viewed from above. FIG.

  As shown in FIG. 6A, an ink guide groove 52 leading from the upstream side of the ink flow to the discharge port 28 is formed on the surface of the discharge port substrate 16 on the ink flow path 30 side, that is, the surface facing the head substrate 12. Is formed. The ink guide groove 52 is inclined at a predetermined angle so that the depth gradually increases from the upstream side of the ink flow toward the ejection port 28. The ink guide groove 52 is provided in the vicinity of the ejection port 28 of each ejection unit.

In this way, by providing the ink guide groove 52 that communicates with the discharge port 28, the ink Q is guided into the discharge port 28 along the ink guide groove 52, so that ink is supplied to the discharge port (ink guide tip). Can be improved. In the conventional ink jet head, since the discharge electrode 18 is provided on the discharge port substrate 16, in order to form such an ink guide groove 52, it is necessary to communicate with the discharge port 28 while avoiding the discharge electrode. However, since the ink jet head of the present invention shown in FIG. 6 is provided with the discharge electrode 18 on the head substrate 12 and the discharge electrode 18 does not exist on the discharge port substrate 16, the ink guide groove 52 is avoided while avoiding the discharge electrode. The ink guide groove 52 can be formed on the discharge port substrate 16 more easily than in the prior art.
In addition, since the discharge electrode 18 is provided on the head substrate 12, an electric field (downward electric field in the drawing) from the discharge port 28 toward the surface of the head substrate 12 acts on the ink particles in the main flow path 30 in most cases. As a result, the ink particles circulating in the main flow path 30 can be quickly aggregated in the ejection port 28. Therefore, according to the inkjet head of the present invention, the responsiveness of the ejection frequency at the time of image recording is improved, and a dot of a desired size can be stably drawn even if dots are drawn continuously at a high speed.

  As shown in FIG. 7, the ink guide groove 52 may be formed at a constant depth over the ink flow direction. In this case, the ink flow supplied from the ink flow path 48 to the inside of the ink guide groove 52 temporarily becomes a turbulent flow due to the step between the surface of the insulating layer 32 and the bottom surface of the ink guide groove 52. The length L of the ink guide groove 52 (length in the ink flow direction) L is preferably 6 times or more, and more preferably 8 times or more the depth D of the ink guide groove 52. .

  The length, width, depth, planar shape, cross-sectional shape, and the like of the ink guide groove 52 are not limited at all. However, the ink supply property to the ejection port changes according to these settings, and therefore, as necessary. It is preferable to set appropriately.

  For example, as described above, when the ink guide groove 52 is not inclined, the length L of the ink guide groove 52 is preferably 6 times or more the depth D, but the ink guide groove 52 is inclined. In this case, the occurrence of turbulent ink flow can be reduced, so that there is an advantage that the length of the ink guide groove can be made shorter than when the ink guide groove 52 is not inclined.

  In addition, the width of the ink guide groove 52 is preferably substantially equal to the diameter of the discharge port 28, but it may be slightly larger or slightly smaller than the diameter of the discharge port 28 as compared with the case where the ink guide groove 52 is not provided. Thus, the ink supply property can be improved reliably.

  The shape of the ink guide groove 52 may be a uniform width in the direction of the ink flow as in the above embodiment, or the width may be narrowed toward the upstream side of the ink flow, The width may become narrower toward the discharge port 28 side. In addition, the cross-sectional shape of the ink guide groove 52 is preferably a trapezoidal shape or an inverted triangular shape that gradually becomes narrower as the depth increases (toward the bottom surface).

  In addition, the ink guide groove 52 may be composed of a single groove or a plurality of grooves toward the through hole 38. In addition, although the ink guide groove is formed on both the upstream side and the downstream side of the ejection port, it may be formed only on the upstream side or only on the downstream side.

  Further, the means for forming the ink guide groove 52 is not limited at all, and any conventionally known excavation means such as dicing, laser processing, sandblasting, etc. can be used depending on the material of the discharge port substrate 16.

FIG. 8 is a conceptual diagram of still another example of the ink jet head of the present invention. FIGS. 9A and 9B are a perspective view of the vicinity of the ink guide of the ink jet head shown in FIG. 8 and a schematic of the vicinity of the ink guide. A cross-sectional view is shown.
The ink jet head 130 shown in FIGS. 8 and 9 has an ink guide weir 50 for guiding the ink circulating through the main flow path 30 to the discharge port 28, and a semicircular discharge electrode (hereinafter referred to as an ink guide weir 50). 6) (except for the semicircular discharge electrode), the ink jet head 120 has the same structure as the ink jet head 120 shown in FIG. In the inkjet head 130 shown in FIGS. 8 and 9, the same members as those in the inkjet head 120 shown in FIG. 6 are denoted by the same reference numerals, and only differences from the inkjet head 120 shown in FIG. In FIG. 9, only the head substrate 12, the ink guide 14, and the ink guide weir 50 are shown for convenience of explanation.

  The ink guide weir 50 is the ink flow direction (arrow a direction) of the ink guide 14 disposed at a position corresponding to the ejection port 38 on the ink channel 48 side surface of the head substrate 12, that is, the bottom surface of the ink channel 48. Upstream and downstream of the nozzle, and gradually approach the discharge port substrate 14 from the vicinity of the position corresponding to the discharge port 38 toward the position corresponding to the center of the discharge port 38 in the ink flow direction. Thus, it has the inclined surface (henceforth an inclined surface) 50a. That is, the ink guide weir 50 has an inclined surface 50 a that intersects the surface of the head substrate 12 at a predetermined angle. The inclined surface 50 a of the ink guide weir 50 can guide the ink circulating through the main flow path 30 to the ejection port 28.

  As shown in FIG. 9, semicircular discharge electrodes 18 a and 18 b are formed on the inclined surface 50 a of the ink guide weir 50. Here, the semicircular discharge electrode 18 is formed on the inclined surface 50a of the ink guide. However, the electrical wiring for electrically connecting the discharge electrodes 18a and 18b to the upper surface 14b of the support portion supporting the ink guide 14. To form a ring-shaped electrode. Alternatively, an electrode is configured by forming a conductive material such as metal by vapor deposition or the like on all the surfaces of the inclined surface 50a and the side wall surface 50b of the ink guide weir 50 and the side wall surface 14b of the support portion of the ink guide 14. Also good.

  Here, the semicircular discharge electrodes 18 a and 18 b are formed on the inclined surface 50 a of the ink guide weir 50 so as to be in contact with the ink Q circulating in the main flow path 30, but exposed to the main flow path 30. The discharge electrodes 18 a and 18 b may be formed inside the ink guide weir 40 so as not to cause a problem.

  Further, the ink guide weir 50 has a shape having a wall surface 50b having substantially the same width as the ejection port 28 and perpendicular to the bottom surface in the direction orthogonal to the ink flow. In addition, the ink guide weir 50 does not block the ejection port 28, and the ink Q weir 50 is secured at a predetermined interval from the surface on the main channel 30 side of the ejection port substrate 16, that is, the upper surface of the main channel 30 so as to secure the channel of the ink Q. It is set apart. Such an ink guide weir 50 is provided in each discharge part.

  As described above, the ink guide weir 50 having a slope inclined toward the ejection port 28 along the ink flow direction is provided on the bottom surface of the main channel 30 (the surface of the head substrate 12 facing the ejection substrate). As a result, an ink flow toward the ejection port 28 is formed, and the ink Q is guided to the opening of the ejection port 28 on the main flow path 30 side. Therefore, the ink Q can be suitably flown into the ejection port 28, and the ink supply property to the ink guide front end portion 14a serving as the ejection portion of the ink droplet R can be improved. Furthermore, the color material particles contained in the ink Q are pushed up toward the ejection port 28 by the electrostatic force from the ejection electrodes 18 a and 18 b provided on the inclined surface 50 a of the ink guide weir 50. Therefore, the responsiveness of the ejection frequency during image recording is improved, and a dot of a desired size can be stably drawn even if dots are drawn continuously at a high speed.

In addition, the ink Q can be prevented from staying inside the discharge port 28, and the discharge port 28 can be prevented from being clogged.
By the way, in FIG. 9, the discharge electrode 18a existing on the upstream side of the ink flow of the discharge port 28 has an electric field that hinders the supply of ink particles to the vicinity of the discharge port when a drive voltage is applied to the discharge electrode 18a. Form. On the other hand, since the discharge electrode 18b existing on the downstream side of the ink flow of the discharge port 28 acts to keep the ink particles in the vicinity of the discharge port, it has a good effect on the supply of the ink particles to the discharge port 28. Play. Therefore, when the discharge electrode is formed on the ink guide weir, it is preferable that the discharge electrode is always installed on the downstream side of the ink flow and the discharge electrode is arbitrarily installed on the upstream side of the ink flow.
Here, the discharge electrode formed on the ink guide weir is a semicircular discharge electrode. However, the discharge electrode is not limited to this shape, and may be a parallel electrode having an arbitrary shape such as a rectangular shape or a semi-elliptical shape. it can. Since the circular electrode has better electric field convergence efficiency than the parallel electrode, it is preferably a circular shape to efficiently form a strong electric field at the tip of the ink guide.

  The length s in the ink flow direction of the ink guide weir 50 may be set as appropriate so that the ink Q can be suitably guided to the ejection port 28 within a range not interfering with the adjacent ejection unit. As shown in FIG. 5, it is preferable that the height t of the highest part of the ink guide weir 50 is 3 times or more (s / t ≧ 3), and more preferably 8 times or more (s / t ≧ 8). preferable.

  The width of the ink guide weir 50 in the direction orthogonal to the ink flow is preferably equal to or slightly wider than the ejection port 28. Further, the width of the ink guide weir 50 is not limited to a uniform one as shown in the drawing, and may be one in which the width gradually decreases or one in which the width gradually increases. Further, the side wall surface 50b is not limited to a vertical surface, and may be an inclined surface or the like.

  The inclined surface (ink guiding surface) 50a of the ink guiding weir 50 may be a shape suitable for guiding the ink Q to the ejection port 38, and may be a slope having a certain inclination angle, or an inclination angle. It may be a surface that changes or a curved surface. Further, the surface is not limited to a smooth surface, and one or more wrinkles or grooves may be formed in the ink flow direction or radially toward the center of the ejection port 38. In this case, the ejection electrode 18 can be formed in a shape corresponding to the inclined surface 50 a of the ink guide weir 50.

  Further, the vicinity of the connection portion with the ink guide 14 on the upper part of the ink guide weir 50 may have a smoothly connected shape without a step as in the illustrated example.

  In the illustrated example, the ink guide weir 50 is arranged on the upstream side and the downstream side of the ink guide 14, but a trapezoidal ink guide weir 50 having inclined surfaces on the upstream side and the downstream side of the ejection port 38 is provided, The ink guide 14 may be erected on the upper portion, or the ink guide 14 and the ink guide weir 50 may be integrally formed. As described above, the ink guide weir 50 may be separately or integrally formed with the ink guide 14 and attached to the head substrate 12, or the head substrate 12 may be shaved by a conventionally known excavation means. It may also be formed.

  The ink guide weir 50 only needs to be provided on the upstream side of the ejection port 28, but the height in the ejection direction of the ink droplets R is also ejected on the downstream side of the ejection port 28 as shown in the illustrated example. It is preferable to be provided so as to become lower as the distance from the outlet 28 increases. As a result, the ink Q guided toward the ejection port 28 by the upstream ink guide weir 50 flows smoothly to the downstream side, so that the ink Q can be kept stable without being turbulent. , Discharge stability can be maintained.

  8 and 9, the ink guide weir 50 is disposed on the upper surface of the head substrate 12. However, as shown in FIG. 10, an ink flow groove 57 is provided in the head substrate 12, An ink guide weir 50 may be disposed inside the ink flow groove 52.

  In the form shown in FIG. 10, an ink flow groove 57 having a predetermined depth passing through a position corresponding to the ejection port 28 is provided along the ink flow direction (arrow a direction). Further, the distance between the upper surface of the head substrate 12 other than the ink flow grooves 57 and the lower surface of the ejection port substrate 16 is narrower than the distance between both in FIGS. As described above, by providing the ink flow groove 57, most of the ink Q flowing through the main flow path 30 can be selectively flowed to the ink flow groove 57.

  An ink guide weir 50 having an inclined surface that inclines toward the discharge port 38 along the ink flow direction is provided at a position corresponding to the discharge port 28 of the ink flow groove 57. The ink Q flowing through the ink flow groove 57 is guided to the ejection port 28 by the ink guide weir 50. Thereby, the ink Q can be suitably flown into the discharge port 28, and the ink supply property to the ink guide tip portion 14a can be improved.

The ink flow groove 57 and the ink guide weir 50 can be formed by processing the head substrate 12 by a conventionally known cutting means.
In the above example, the ink guide groove 52 is formed on the discharge port substrate 16 and the ink guide weir 50 is provided on the head substrate 12. However, the ink guide groove 52 is not formed on the discharge port substrate 16. In addition, the head substrate 12 may be provided with only the ink guide weir 50.

Next, the ink used for the inkjet head of the present invention will be described.
The ink Q (ink composition) used in the ink jet head of the present invention is obtained by dispersing coloring material particles (including coloring material and charged fine particles) in a carrier liquid.
In addition, the ink Q may appropriately contain dispersed resin particles for improving the fixability of the image after printing together with the color material particles.

The carrier liquid is preferably a dielectric liquid (nonaqueous solvent) having a high electric resistivity (10 ⁹ Ω · cm or more, preferably 10 ¹⁰ Ω · cm or more). When the electric resistance of the carrier liquid having a low electric resistivity is low, the carrier liquid itself is charged by charge injection due to the voltage applied by the discharge electrode 18, so that the coloring material particles are not concentrated. In addition, a carrier liquid having a low electrical resistivity is not suitable for the present invention because there is a concern that electrical conduction between adjacent ejection electrodes 18 may occur.

The relative dielectric constant of the dielectric liquid used as the carrier liquid is preferably 5 or less, more preferably 4 or less, and still more preferably 3.5 or less. By setting the relative dielectric constant in such a range, an electric field effectively acts on the colorant particles in the carrier liquid, and migration easily occurs.
Note that the upper limit value of the specific electric resistance of such a dielectric liquid is preferably about 10 ¹⁶ Ωcm, and the lower limit value of the relative dielectric constant is preferably about 1.9. The reason why it is desirable that the electric resistance of the dielectric liquid is in the above range is that if the electric resistance is low, ink ejection under a low electric field is deteriorated, and that the relative dielectric constant is preferably in the above range. This is because when the dielectric constant increases, the electric field is relaxed by the polarization of the solvent, and the color of the dots formed thereby becomes light or causes blurring.

  The dielectric liquid used as the carrier liquid is preferably a linear or branched aliphatic hydrocarbon, alicyclic hydrocarbon, or aromatic hydrocarbon, and halogen-substituted products of these hydrocarbons. For example, hexane, heptane, octane, isooctane, decane, isodecane, decalin, nonane, dodecane, isododecane, cyclohexane, cyclooctane, cyclodecane, benzene, toluene, xylene, mesitylene, Isopar C, Isopar E, Isopar G, Isopar H, Isopar M, Isopar L (isopar: trade name of Exxon), Shellsol 70, Shellsol 71 (shellsol: trade name of Shell Oil), Amsco OMS, Amsco 460 Solvent (trade name of Amsco: Spirits), Silicone oil (for example, KF-96L manufactured by Shin-Etsu Silicone) or the like can be used alone or in combination.

The color material particles dispersed in such a carrier liquid may be dispersed in the carrier liquid as the color material itself as the color material particles, or may be contained in the dispersed resin particles for improving the fixability. When contained in the dispersed resin particles, the pigment is generally coated with the resin material of the dispersed resin particles to obtain resin-coated particles, and the dye is a colored particle by dispersing the dispersed resin particles. Etc. are common.
As the color material, any pigments and dyes that have been conventionally used in inkjet ink compositions, printing (oil-based) ink compositions, or electrophotographic liquid developers can be used.

  In the ink Q, the content of the color material particles (the total content of the color material particles or further dispersed resin particles) is preferably contained in the range of 0.5 to 30% by weight with respect to the whole ink, and more preferably. Is preferably contained in the range of 1.5 to 25% by weight, more preferably 3 to 20% by weight. If the content of the colorant particles is reduced, problems such as insufficient printed image density or difficulty in obtaining a strong image due to difficulty in obtaining the affinity between the ink Q and the surface of the recording medium P are likely to occur. On the other hand, when the content is increased, it becomes difficult to obtain a uniform dispersion, or the ink Q is easily clogged with the inkjet head 10 or the like, and it is difficult to obtain stable ink discharge. is there.

As the pigment used as the color material, regardless of inorganic pigments or organic pigments, those generally used in the technical field of printing can be used. Specifically, for example, carbon black, cadmium red, molybdenum red, chrome yellow, cadmium yellow, titanium yellow, chromium oxide, viridian, cobalt green, ultramarine blue, Prussian blue, cobalt blue, azo pigment, phthalocyanine pigment Conventionally known pigments such as quinacridone pigments, isoindolinone pigments, dioxazine pigments, selenium pigments, perylene pigments, perinone pigments, thioindigo pigments, quinophthalone pigments, metal complex pigments, and the like are not particularly limited. Can be used.
As dyes used as coloring materials, azo dyes, metal complex dyes, naphthol dyes, anthraquinone dyes, indigo dyes, carbonium dyes, quinoneimine dyes, xanthene dyes, aniline dyes, quinoline dyes, nitro dyes, nitroso dyes, benzoquinone dyes, naphthoquinone dyes And oil-soluble dyes such as phthalocyanine dyes and metal phthalocyanine dyes.

  The average particle diameter of the colorant particles dispersed in the carrier liquid is preferably 0.1 to 5 μm, more preferably 0.2 to 1.5 μm, and still more preferably 0.4 to 1.0 μm. . This particle size is determined by CAPA-500 (trade name, manufactured by Horiba, Ltd.).

After the colorant particles are dispersed in the carrier liquid, the charge material is added to the carrier liquid to charge the colorant particles, whereby the ink Q is obtained by dispersing the charged colorant particles in the carrier liquid. In addition, you may add a dispersion medium as needed at the time of dispersion | distribution of colored fine particles.
As an example of the charge control agent, various materials used in electrophotographic liquid developers can be used. Also, “Recent development and commercialization of electrophotographic development systems and toner materials”, pages 139 to 148, “The Basics and Applications of Electrophotographic Technology” edited by Electrophotographic Society, pages 497 to 505 (Corona Inc., published in 1988), Yuji Harasaki Various charge control agents described in “Electrophotography” 16 (No. 2), p. 44 (1977) can also be used.

The color material particles may be positively charged or negatively charged as long as they have the same polarity as the driving voltage applied to the ejection electrode 18.
The charge amount of the color material particles is preferably in the range of 5 to 200 μC / g, more preferably 10 to 150 μC / g, and still more preferably 15 to 100 μC / g.

In addition, since the electric resistance of the dielectric solvent may change due to the addition of the charge control agent, the distribution ratio P defined below is preferably 50% or more, more preferably 60% or more, and even more preferably 70% or more. And
P = 100 × (σ1−σ2) / σ1
Here, σ1 is the electrical conductivity of the ink Q, and σ2 is the electrical conductivity of the supernatant obtained by applying the ink Q to the centrifuge. The electrical conductivity was measured using an LCR meter (AG-4311 manufactured by Ando Electric Co., Ltd.) and an electrode for liquid (LP-05 type manufactured by Kawaguchi Electric Manufacturing Co., Ltd.) under the conditions of an applied voltage of 5 V and a frequency of 1 kHz. This is the measured value. Centrifugation was performed for 30 minutes using a small high-speed cooling centrifuge (Tomy Seiko Co., Ltd. SRX-201) under conditions of a rotational speed of 14500 rpm and a temperature of 23 ° C.
By using the ink Q as described above, migration of the color material particles is likely to occur and the concentration is facilitated.

The electrical conductivity of the ink Q is preferably 100 to 3000 pS / cm, more preferably 150 to 2500 pS / cm, and still more preferably 200 to 2000 pS / cm. By setting the electric conductivity in the above range, the voltage applied to the ejection electrode does not become extremely high, and there is no fear of causing electrical continuity between adjacent recording electrodes.
The surface tension of the ink Q is preferably in the range of 15 to 50 mN / m, more preferably 15.5 to 45 mN / m, and still more preferably 16 to 40 mN / m. By setting the surface tension within this range, the voltage applied to the ejection electrode does not become extremely high, and the ink does not leak around the head and become contaminated.
Furthermore, the viscosity of the ink Q is preferably 0.5 to 5 mPa · sec, more preferably 0.6 to 3.0 mPa · sec, and still more preferably 0.7 to 2.0 mPa · sec.

In the present invention, it is a solid component mainly dispersed in a carrier liquid, rather than causing the ink to fly toward the recording medium by applying a force to the entire ink as in the conventional ink jet system. A force is applied to the color material particles to fly.
As a result, images can be recorded on various recording media P such as plain paper and non-absorbing films (for example, PET film), and bleeding and flow are generated on the recording media P. Therefore, high-quality images can be obtained on various recording media.

FIG. 11 shows a conceptual diagram of an embodiment of the ink jet recording apparatus of the present invention using the ink jet head of the present invention.
An inkjet recording apparatus 60 (hereinafter, referred to as a printer 60) shown in FIG. 1 is an apparatus that performs four-color printing on one side of a recording medium P, and includes a recording medium P conveying means, an image recording means, and a solvent recovery means. These are housed in a housing 61.
The conveying means includes a feed roller pair 62, a guide 64, rollers 66 (66a, 66b and 66c), a conveying belt 68, a conveying belt position detecting means 69, an electrostatic adsorption means 70, a static eliminating means 72, a peeling means 74, and a fixing. -It has the conveyance means 76 and the guide 78. The image recording forming unit includes a head unit 80, an ink circulation system 82, a head driver 84, and a recording medium position detecting unit 86. Further, the solvent recovery means includes a discharge fan 90 and a solvent recovery device 92.

  In the conveyance means for the recording medium P, the feed roller pair 62 is a conveyance roller pair provided adjacent to the carry-in port 61 a provided on the side surface of the housing 61. The feed roller 62 feeds the recording medium P supplied from a stocker (not shown) to the transport belt 68 (portion supported by the roller 66a). The guide 64 is provided between the feed roller pair 62 and a roller 66 a that supports the conveyance belt 68, and guides the recording medium P to the conveyance belt 68.

It should be noted that a foreign matter removing means for removing foreign matter such as dust and paper dust adhering to the recording medium P is preferably provided in the vicinity of the feed roller pair 62.
As the foreign matter removing means, one or more of non-contact methods such as known suction removal, blow-off removal, electrostatic removal, and contact methods using brushes, rollers, etc. may be used in combination. Alternatively, the feed roller pair 62 may be a slightly adhesive roller, and a cleaner for the feed roller pair 62 may be provided to remove foreign matters such as dust and paper powder when the recording medium P is fed by the feed roller pair 62.

The conveyor belt 68 is an endless belt stretched around the three rollers 66. At least one of the rollers 66a, 66b, and 66c is connected to a drive source (not shown), and rotates the conveyor belt 68.
The conveyance belt 68 functions as a platen for holding the recording medium P in addition to the scanning conveyance means for the recording medium P during image recording by the head unit 80, and further conveys the image to the fixing / conveyance means 76 after image recording. Therefore, the transport belt 68 is preferably formed of a material having excellent dimensional stability and durability. For example, the transport belt 68 is formed of a metal, a polyimide resin, a fluororesin, another resin, or a composite thereof.

In the illustrated example, since the recording medium P is held on the conveyance belt 68 by electrostatic attraction, the conveyance belt 68 is insulative on the side (front surface) that holds the recording medium P and is in contact with the roller 66 (back surface). ) Has conductivity. In the illustrated example, the roller 66a is a conductive roller, and the back surface of the transport belt 68 is grounded via the roller 66a.
That is, the conveyance belt 68 functions as the counter electrode 24 composed of the electrode substrate 24a and the insulating sheet 24b shown in FIG. 1 when holding the recording medium P.

As such a conveyor belt 68, a resin sheet and a metal belt are bonded to each other with a belt coated with any of the above resin materials, an adhesive, etc. A belt having a metal layer and an insulator layer manufactured by various methods such as a metal belt or a belt formed by metal vapor deposition on the back surface of a belt made of the above resin may be used.
Further, it is preferable that the surface of the conveying belt 68 that contacts the recording medium P is smooth, and thereby, good adsorbability of the recording medium P can be obtained.

  The conveyor belt 68 is preferably suppressed from meandering by a known method. As a meandering suppression method, for example, the roller 66c is a tension roller, and the axis of the roller 66c is adjusted between the roller 66a and the roller 66b in accordance with the output of the conveying belt position detecting means 69, that is, the detecting position in the width direction of the conveying belt 68. A method of suppressing meandering by changing the tension at both ends in the width direction of the conveyor belt by tilting with respect to the axis is exemplified. Further, the meandering may be suppressed by forming the roller 66 in a tapered shape, a crown shape, or other shapes.

  Here, as described above, the conveying belt position detecting unit 69 suppresses the meandering of the conveying belt and regulates the position of the recording medium P in the scanning conveying direction at the time of image recording to a predetermined position. 68 is used to detect the position in the width direction, and known detection means such as a photosensor is used.

The electrostatic attraction means 70 applies a predetermined bias voltage to the head unit 80 (the ink jet head of the present invention) to the recording medium P and attracts it to the conveying belt 68 by electrostatic force to hold it. Is charged to a predetermined potential.
In the illustrated example, the electrostatic attraction unit 70 includes a scorotron charger 70a that charges the recording medium P, and a negative high-voltage power supply 70b that is connected to the scorotron charger 70a. While the recording medium P is conveyed by the feed roller pair 62 and the conveying belt 68, the recording medium P is charged with a negative bias voltage by the scorotron charger 70a connected to the negative high voltage power source 70b, and is applied to the insulating layer of the conveying belt 68. It is electrostatically attracted.

In addition, the conveyance speed of the conveyance belt 68 when charging the recording medium P may be in a range that can be stably charged, and may be the same as or different from the conveyance speed at the time of image recording. Alternatively, the recording medium P may be rotated a plurality of times so that the electrostatic adsorption means acts on the same recording medium P a plurality of times to perform uniform charging.
In the illustrated example, the electrostatic adsorption unit 70 performs electrostatic adsorption and charging of the recording medium P. However, the electrostatic adsorption unit and the charging unit may be provided separately.

  The electrostatic attraction means is not limited to the illustrated scorotron charger 70a, and various other means and methods such as a corotron charger, a solid charger, and a discharge needle can be used. Further, as will be described in detail later, at least one of the rollers 66 is a conductive roller, or a conductive platen is provided on the back surface side (opposite side of the recording medium P) of the conveying belt 68 at the recording position on the recording medium P. By arranging and connecting this conductive roller or conductive platen to a negative high voltage power source, the electrostatic attraction means 70 may be configured, or the conveying belt 68 is an insulating belt and the conductive roller is grounded. The conductive platen may be connected to a negative high voltage power source.

The recording medium P charged by the electrostatic attraction means 70 is transported to the position of the head unit 80 described later by the transport belt 68.
The head unit 80 records an image on the recording medium P by ejecting ink droplets according to the image data using the inkjet head of the present invention. Here, the ink jet head of the present invention discharges the ink droplet R by superimposing the drive voltage on the bias voltage by applying the drive voltage to the discharge electrode 18 with the charging potential of the recording medium P as the bias voltage, The image is recorded on the recording medium P as described above. At this time, by providing a heating means for the conveying belt 68 and increasing the temperature of the recording medium P, fixing of the ink droplets R on the recording medium P can be promoted, and bleeding is further suppressed and image quality is improved. Can be achieved.
The image recording by the head unit 80 or the like will be described in detail later.

The recording medium P on which the image is recorded is discharged by the discharging unit 72, peeled off from the transport belt 68 by the peeling unit 74, and transported to the fixing / transporting unit 76.
In the illustrated example, the static elimination unit 72 is a so-called AC corotron static eliminator having a corotron static eliminator 72a, an AC power source 72b, and a DC high-voltage power source 72c grounded at one end. In addition to the above, as the static elimination means, various means and methods such as a scorotron static eliminator, a solid charger, a discharge needle, etc. can be used, and a conductive roller, A configuration using a conductive platen is also preferably used.
As the peeling means 74, a known technique such as a peeling blade, a reverse rotation roller, an air knife or the like can be used.

The recording medium P peeled off from the conveying belt 68 is sent to the fixing / conveying means 76, and the image formed by ink jet is fixed. A roller pair including a heat roller 76a and a conveyance roller 76b is used as the fixing / conveying means 76, and the recorded image is heated and fixed while the recording medium P is nipped and conveyed.
The recording medium P on which the image is fixed is guided by a guide 78 and discharged to a discharge stocker (not shown).

Examples of the heat fixing means include general heat fixing such as irradiation with infrared rays or a halogen lamp or a xenon flash lamp, or hot air fixing using a heater, in addition to the heat roll fixing described above. In the heat fixing / conveying means 76, the heating means performs only heating, and the conveying means and the heat fixing means may be provided separately.
In the case of heat fixing, when coated paper or laminated paper is used as the recording medium P, a phenomenon called blistering occurs in which the water inside the paper rapidly evaporates due to a rapid temperature rise and the paper surface is uneven. May occur. In order to prevent this, it is preferable to arrange a plurality of fixing devices and change one or both of the power supply of each fixing device and the distance to the recording medium P so that the temperature of the recording medium P gradually increases.

The printer 60 is preferably configured so that nothing touches the image recording surface of the recording medium P from at least the image recording by the head unit 80 until the fixing by the fixing / conveying means 76 is completed.
Further, the moving speed of the recording medium P at the time of fixing in the fixing / conveying means 76 is not particularly limited, and may be the same as or different from the conveying speed by the conveying belt 68 at the time of image formation. . When the conveyance speed is different from that at the time of image formation, it is preferable to provide a speed buffer for the recording medium P immediately before the fixing / conveyance means 76.

Hereinafter, image recording in the printer 60 will be described in detail.
As described above, the image recording means of the printer 60 includes the head unit 80 that discharges the ink jet, the ink circulation system 82 that supplies and recovers the ink Q to the head unit 80, a computer (not shown), a RIP (Raster Image Processor), and the like. A head driver 84 that drives the head unit 80 by an output image signal from an external device, and a recording medium position detecting unit 86 that detects the recording medium P in order to determine the image recording position in the recording medium P are configured.

FIG. 11B is a perspective view schematically showing the head unit 80 and the conveying means for the recording medium P around it.
The head unit 80 has four inkjet heads 80a corresponding to ink ejection of four colors of cyan (C), magenta (M), yellow (Y), and black (K) for recording a full color image. Then, in accordance with a signal from the head driver 84 supplied with the image data, the ink Q supplied by the ink circulation system 82 is ejected as an ink droplet R, and the recording medium P being conveyed by the conveying belt 68 at a predetermined speed. Record an image on The inkjet heads 80 a for the respective colors are arranged in the conveyance direction of the conveyance belt 68.
The ink jet heads 80a of the respective colors of the head unit 80 are the ink jet heads of the present invention.

In the illustrated example, the inkjet heads 80a are line heads in which the ejection ports 28 are arranged in the entire width direction of the recording medium P, and are preferably arranged in a staggered manner as shown in FIG. A multi-channel head having a plurality of nozzle rows.
Therefore, in the illustrated example, the recording medium P is transported to the head unit 80 in a state where the recording medium P is held on the transport belt 68, and the recording medium P is passed once, that is, only one scanning transport is performed. An image is formed on the entire surface of the recording medium P. Therefore, image recording (drawing) can be performed at a higher speed than when the ejection head is serially scanned.

The ink jet head of the present invention can also be used for a so-called serial head (shuttle type). Therefore, the printer 60 may also be in this mode.
In this case, the head unit 80 is configured by aligning the row of the ejection ports 28 of each inkjet head (which may be single row or multi-channel) with the carrying direction of the carrying belt 68, and the head unit 80 is carried by the recording medium P. Known scanning means for scanning in a direction orthogonal to the direction is provided.
The image recording may be performed in the same manner as a normal shuttle type ink jet printer, and the recording medium P is intermittently conveyed by the conveying belt 68 according to the length of the row of the ejection ports 28 and is synchronized with this intermittent conveyance. Then, at the time of stop, the head unit 80 is scanned to record an image on the entire surface of the recording medium P.
Thus, the image formed on the entire surface of the recording medium P by the head unit 80 is fixed by the fixing / conveying means 76 by the recording medium P being nipped and conveyed by the fixing / conveying means 76 as described above. Is done.

The head driver 84 receives image data from an external device, receives image data from a system control unit (not shown) that performs various processes, and drives the head unit 80 based on the image data.
This system control unit performs color separation, division into appropriate numbers of pixels and gradations, etc. on image data received from external devices such as computers, RIPs, image scanners, magnetic disk devices, and thumbtack data transmission devices. This is a part that is used as image data for the head driver 84 to drive the head unit 80 (inkjet head). Further, the system control unit controls the ink ejection timing by the head unit 80 in accordance with the conveyance timing of the recording medium P by the conveyance belt 68. The discharge timing is controlled by using an output from the recording medium position detecting unit 86 and an output signal from the encoder disposed on the conveying belt 68 or the driving unit of the conveying belt 68.
The recording medium position detection means 86 is for detecting the recording medium P conveyed to the ink droplet ejection position by the head unit 80, and known detection means such as a photo sensor can be used.
Here, the head driver 84 divides the drawing when there are a large number of ejection units (number of channels) to be controlled, such as when a line head is applied, and a known resistance matrix driving method or resistance diode matrix driving method. May be used. Thereby, the number of ICs used by the head driver 84 can be reduced, and the cost can be reduced and the control circuit size can be suppressed.

  The ink circulation system 82 is for flowing the ink Q through the main flow path 30 (see FIG. 2) of the ink jet head 80a of each color of the head unit 80, and is an ink tank for each of four colors (C, M, Y, K). An ink circulating device 82a having a pump, a replenishing ink tank (not shown), and the like, and ink for supplying the ink Q of each color from the ink tank of the ink circulating device 82a to the main flow path 30 of each color inkjet head of the head unit 80 It has a supply system 82b and an ink collection system 82c that collects ink from the main flow path 30 of each color inkjet head of the head unit 80 to the ink circulation device 82a.

The ink circulation system 82 supplies ink Q for each color from the ink tank to the head unit 80 via the ink supply system 80b by the ink circulation device 82a, and for each color from the head unit 80 via the ink supply system 80c. Any ink Q can be used as long as it can be collected and circulated in the ink tank.
The ink tank stores ink Q of each color, and the ink Q is pumped out by a pump and sent to the head unit 80. As the ink is discharged from the head unit 80, the density of the ink circulating in the ink circulation system 82 is decreased. In the ink circulation system 82, the ink density is detected by the ink density detector and replenished accordingly. It is desirable to appropriately replenish ink from the ink tank and maintain the ink density within a predetermined range.

Further, the ink tank is preferably provided with a stirring device for suppressing precipitation / concentration of the solid component of the ink and an ink temperature management device for suppressing temperature change of the ink. The reason for this is that if the temperature is not controlled, the ink temperature will change due to changes in the environmental temperature, etc., and the dot diameter will change due to changes in the ink properties, making it impossible to stably form high-quality images. Because there is.
As the stirring device, a rotary blade, an ultrasonic vibrator, a circulation pump, or the like can be used.
As the ink temperature control device, a known method such as a method in which a heating element such as a heater or a Peltier element or a cooling element is arranged in the head unit 80, ink tank, ink distribution pipe system, etc., and control is performed by a temperature sensor such as a thermostat. Can be used. When the temperature control device is arranged in the ink tank, it is preferable to arrange it together with the stirring device so as to make the temperature distribution constant. Further, the stirring device for keeping the concentration distribution in the tank constant may be shared with the stirring device for suppressing the precipitation and concentration of the solid component of the ink.

As described above, the printer 60 has the solvent recovery means including the exhaust fan 90 and the solvent recovery device 92. The solvent recovery means recovers the carrier liquid that evaporates from the ink droplets ejected from the head unit 80 onto the recording medium P, particularly the carrier liquid that evaporates from the recording medium P when fixing the image formed by the ink droplets. To do.
The discharge fan 90 is for sucking air inside the casing 61 of the printer 60 and sending it to the solvent recovery device 92.
The solvent recovery device 92 includes a solvent vapor absorber, and adsorbs the solvent component of the gas containing the solvent vapor sucked by the exhaust fan 90 to the solvent vapor absorber, and the gas after the solvent is adsorbed and recovered. The paper is discharged out of the casing 11 of the printer 60. As the solvent vapor absorbing material, various activated carbons are preferably used.

  In the above description, an electrostatic ink jet recording apparatus that records a color image using four color inks of C, M, Y, and K has been described. However, the present invention is not limited to this, and a monochrome recording apparatus Alternatively, recording may be performed using an arbitrary number of inks of other colors, for example, light colors or special colors. In that case, the number of head units 80 and ink circulation systems 82 corresponding to the number of ink colors are used.

  In each of the above examples, the ink jet discharges ink droplets R by charging the color material particles in the ink positively and setting the opposite electrode on the back of the recording medium or recording medium P to a negative high voltage. However, the present invention is not limited to this, and conversely, the color material particles in the ink may be negatively charged, and the recording medium or the counter electrode may be set to a positive high voltage to perform image recording by inkjet. . Thus, when the polarity of the colored charged particles is reversed from the above example, the polarity of the voltage applied to the electrostatic adsorption means, the counter electrode, and the drive electrode of the inkjet head may be reversed from the above example. .

  Further, the ink jet head and the recording apparatus of the present invention are not limited to those that discharge ink containing charged color material components, and are not particularly limited as long as they are liquid discharge heads that discharge liquid containing charged particles. For example, in addition to the electrostatic ink jet recording apparatus described above, the present invention can be applied to a coating apparatus that applies charged objects by discharging droplets and applying an object.

  As described above, the electrostatic ink jet head of the present invention and the ink jet recording apparatus using the same have been described in detail. However, the present invention is not limited to the above-described embodiment, and various types can be made without departing from the gist of the present invention. Of course, improvements and changes may be made.

It is a schematic sectional drawing of an example of the inkjet head of this invention. (A) And (B) is a conceptual diagram for demonstrating the inkjet head shown in FIG. It is another example of the inkjet head of this invention, and is a schematic block diagram of the type provided with a discharge electrode inside a head substrate. It is another example of the inkjet head of this invention, and is a schematic block diagram of an inkjet head provided with the discharge electrode of two layers. (A) is a schematic plan view in the surface containing an AA line of the inkjet head shown in FIG. 4, (B) is a schematic plan view in the surface containing a BB line. (A) is another example of the inkjet head of the present invention, and is a schematic configuration diagram of a type in which an ejection guide substrate is provided with an ink guide groove, and (B) is an ejection portion of the inkjet head shown in (A). It is a schematic plan view when viewed from above. It is another example of the inkjet head of this invention, and is a schematic block diagram of the type in which the ink groove with a fixed groove depth was formed in the discharge outlet board | substrate. It is another example of the inkjet head of this invention, and is a schematic block diagram of the type provided with an ink induction weir on a head substrate. (A) is a schematic perspective view of the inkjet head shown in FIG. 8, (B) is a figure explaining the shape dimension of an ink induction weir. It is a schematic perspective view of another example of the inkjet head of this invention provided with an ink guide weir on a head substrate. (A) is a schematic configuration diagram of the ink jet recording apparatus of the present invention, and (B) is a perspective view schematically showing a head unit and a recording medium conveying means in the vicinity thereof. It is a schematic block diagram of the conventional inkjet head. It is a timing chart when applying a drive voltage to a control electrode.

Explanation of symbols

10, 110, 120, 130, 140 Inkjet head 12 Head substrate 14 Ink guide 14a Front end portion 16 Discharge port substrate 18, 18a, 18b Discharge electrode 20 Guard electrode 22 Shield plate 24 Counter electrode 24a Electrode substrate 24b Insulating sheet 26 Charging unit 26a Scorotron charger 26b Bias voltage source 28 Discharge port 30 Main flow path 32 Signal voltage source 34, 35 Insulating layer 36 Opening 50 Ink guide weir 50a Inclined surface 52 Ink guide groove 60 Inkjet printer 62 Feed roller 64 Guide 66 Roller 68 Conveying belt 69 Conveying belt position detecting means 70 Electrostatic attracting means 72 Static eliminating means 74 Peeling means 76 Fixing / conveying means 78 Guide 80 Head unit 82 Ink circulation system 84 Head driver 86 Recording medium position detection Discharging means 90 Discharging fan 92 Solvent recovery device P Recording medium Q Ink R Ink droplet

Claims (15)

An inkjet head that discharges ink as ink droplets using electrostatic force and flies toward a recording medium,
An ejection port substrate having an ejection port through which the ink droplets are ejected; and
A head substrate disposed at a predetermined interval from the discharge port substrate;
An inkjet head comprising: an ejection electrode provided at a position facing the ejection port of the head substrate and applied with an ejection voltage for ejecting the ink.   The inkjet head according to claim 1, wherein the ejection electrode is formed on a surface of the head substrate that faces the ejection port substrate.   The inkjet head according to claim 1, wherein the ejection electrode is formed inside the head substrate.   The said discharge electrode is comprised from the 1st discharge electrode and the 2nd discharge electrode, and the 1st discharge electrode and the 2nd discharge electrode are substantially coaxial, and are arrange | positioned at predetermined intervals. The inkjet head as described in any one of Claims.   The inkjet head according to claim 1, wherein the discharge electrode has a ring shape.   The head substrate includes an ink guide weir for guiding the ink to the discharge port in the vicinity of a position facing the discharge port, and the discharge electrode is formed on the ink guide weir. The inkjet head according to any one of 5.   The inkjet head according to claim 1, wherein the ink guide weir has an inclined surface, and a ring-shaped ejection electrode is formed on the inclined surface.   The ink jet head according to any one of claims 1 to 7, wherein an ink guide groove connected to the discharge port is formed on a surface of the discharge port substrate facing the head substrate.   The inkjet head according to claim 8, wherein the ink guide groove has a shape in which the groove depth increases toward the ejection port. An ink guide provided at a position of the head substrate facing the discharge port of the discharge port substrate, the tip of which penetrates the discharge port;
The inkjet head according to claim 1, wherein the ejection electrode is formed so as to surround a connection portion between the ink guide and the head substrate.   The inkjet head according to claim 10, wherein a ratio between an inner diameter of the ejection electrode and a distance from the ejection electrode to a tip of the ink guide is in a range of 1: 0.5 to 1: 2.   Furthermore, it has a guard electrode for shielding the electric field which generate | occur | produces from the said discharge electrode, The said guard electrode is formed in the position near the said recording medium rather than the said discharge electrode. The inkjet head as described.   The inkjet head according to claim 12, wherein the guard electrode is formed inside the ejection substrate. Furthermore, a power supply for applying a discharge voltage to the discharge electrode is provided,
The wiring connected to the said power supply from the said discharge electrode is formed in the surface on the opposite side to the surface opposite to the said discharge port board | substrate of the said head board | substrate. Inkjet head.   An ink jet recording apparatus comprising the ink jet head according to claim 1.

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